The present invention relates to a grinding machine for sharpening (honing) blades of knives, scissors, hand tools or the like, with a magazine, a feed station or similar, and with a honing station for the blades, which has two contrarotating grinding wheels. The invention furthermore relates to a method of sharpening blades that can be performed using such a machine. The said method comprises the following main operations: take-up of a blade from the magazine, the feed station or the like, feeding into the honing station, honing of the blade, depositing of the blade.
Machines of the said type have long been known, but sharpening (honing) of the blades on these is still performed manually, which entails high labour costs. This is due, among other thing s, to the large number of blades to be machined, with different cutting edge contour geometry that necessitates individual machining when applying the blade between the grinding wheels and when following the outline of the cutting edge contour during sharpening. Correct honing calls for much skill and experience on the part of the operative working on this.
The object of the present invention is to automate the honing of blades, the intention being to ensure a high dimensional accuracy for the different blade shapes, so that the carrying out of the machining process can be simplified and shortened whilst maintaining a high working accuracy of the machine.
According to the invention this is achieved by a robot with memory-programmable control having a manipulator moveable in at least four of the six possible translatory and rotational degrees of spatial freedom, a gripper head, which has a holding device for accommodating and moving a blade, being fixed to the manipulator.
The robot with memory-programmable control allows the geometric and production-engineering information, obtained from the design drawing or by measuring workpieces to be machined, to be fed into the system using a higher level programming language. From this an integral computer calculates the corresponding parts program with the various infeed and working movements for the manipulator including the gripper head.
In the method according to the invention all the aforementioned main operations, blade take-up, feeding into the honing station, honing of the blade and depositing of the blade, are therefore carried out by means of the robot with memory-programmable control using its moveable manipulator, the blades being accommodated in the holding device of the gripper head fixed to the manipulator.
At the same time, the method according to the invention proposes that the cutting edge contour preferably be approximated by radii over the length of the cutting edge, in each case between selected, succeeding support points, the radius value xe2x80x9cinfinitexe2x80x9d being assigned to a straight contour section in the area between two adjacent support points (of a pair of support points). The invention can thus be used not only for butcher""s knives, but advantageously also for sharpening blades with convex and concave contour sections, like those of certain boning knives, for example, a high degree of efficiency being achieved especially in large and medium-scale series production.
An especially advantageous embodiment of the invention resides in equipping the gripper head with a device for applying an adjustable force to a blade clamped in the holding device. In this way it is possible to replicate, in automated form, the pressure of the cutting edge of the blade against the grinding wheel that is applied in manual grinding. The application of a constant force has proved especially advantageous here, the optimum magnitude of which force may be empirically determined by prior experiment according to the cutting edge thickness and the material characteristics of the blade, especially its hardness. In contrast to manual honing, precisely defined forces can be set in this way. The honing cycle time is also advantageously no longer determined subjectively and is hence not subject to fluctuations.
The device for applying force to the blade clamped in the holding device may at the same time preferably have a piston-cylinder unit, especially a pneumatic one, with pressure regulator, for generating force. In this way the force can be applied rapidly and precisely, the use of a pneumatic device having the additional advantage that the compressed fluid has a certain cushioning action, that is to say an elastic damping effect, which benefits the machining process.
A further, extremely advantageous design feature of the grinding machine according to the invention consists of designing the holding device in such a way that the blade clamped therein can be fixed in its longitudinal and vertical height directions, but is laterally displaceable and tiltable in the direction of its thickness. This avoids the necessity of having to compile a modified control program if tolerances occur in the unmachined blanks supplied, or parts to be machined with an identical contour present slight positional differences in clamping, for example in their angular position relative to the machine table. Such a design construction of the holding device has the practical advantage that when honing, self-centring of the blade occurs due to the forces exerted by the contra-rotating grinding wheels.